1. Field of the Invention
The present invention relates to a driving circuit, and more particularly but not by any way of limitation, to a driving circuit having a passive-type power factor correction (PFC) function, utilized in illuminating element, especially in LED (light emitting diode).
2. Related Art
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power and is a dimensionless number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf=50% pf). Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power will be greater than the real power.
Through the environment/economization policies driven by the governments around the world, LED is well-developed and applied to two major applications including display and illumination functions. Due to plenty of nonstop technology advancements, the conventional single-color LED is gradually unable to satisfy human's visual needs. Consequently, advanced LED products such as bicolor LED and full-color LED are developed afterwards.
With the push toward more efficient energy usage, lower carbon footprints and resource sustainability gaining momentum throughout the world, virtually every aspect of energy generation and consumption is coming under intense scrutiny for improvement Much of the media buzz has centered upon such “big picture” sweeping changes as smart power grids, wind and solar power, carbon sequestration, etc. Reducing energy consumption and increasing energy efficiency are among the European Union's main goals. At the end of 2008, the European Parliament and European Council wrote into EU law three ambitious targets for 2020: cutting greenhouse gases by 20% (30% if international agreement is reached), supplying 20% of energy from renewable sources, and reducing energy consumption by 20% through energy efficiency. Therefore, how to enhance the power factor (PF) of LED is an important issue.